1. Field of the Invention
The present invention relates to a numerically controlled machine tool for machining a workpiece according to a command entered from a keyboard or the like, and more specifically, to a numerically controlled machine tool provided with a machine control console including a keyboard, changeover switches and the like.
2. Description of the Related Art
Recently, a keyboard and switches such as changeover switches and the like on a machine control console provided for a numerically controlled machine tool give a feeling of operation by emitting an LED (light emitting diode) when they are pressed. The light emitting diode is particularly useful when a switch difficult to give a feeling of operation such as a flat key switch is pressed.
In general, an on/off state of switches on a machine control console is determined by means of a matrix. The determination of the on/off state is carried out in such a manner that the switches are caused to correspond to the points of intersections on the matrix and a common signal is supplied to each common line. Conventionally, a numerical control apparatus includes driving circuits for supplying a signal to each of the switches on the machine control console and receiving circuits for receiving signals from the machine control console.
Nevertheless, a problem arises in that when the number of signal lines increases between the machine control console and the numerical control apparatus, a noise such as an impulse or the like is liable to be mixed to the signal lines particularly in a factory where the numerical control apparatus is installed and faulty operation of a machine tool is caused by it. Further, another problem arises in that since as many driving circuits and receiving circuits as the number of signal lines are required, cost increases.